The present invention relates to a belt transfer type image forming apparatus for use in an electro-photographic copying machine, printer, etc., and more particularly to a belt transfer type image forming apparatus for use in a four-drum tandem type color copying machine and color printer.
A most known technique relating to a transfer section of a prior-art electrophotographic image forming apparatus is a transfer technique using a corona charger disposed to face a photosensitive drum.
However, harmful ozone is generated in this method.
As an ozone-free transfer technique, a contact-type transfer technique is known. Jpn. Pat. Appln. KOKAI Publication No. 6-110343 discloses a technique for performing transfer using a semiconducting transfer belt and a transfer roller disposed on the back side of the transfer belt. In this technique, transfer is effected by applying a transfer bias to the transfer roller.
Color image forming apparatuses for forming color images of plural toners of color components Y (yellow), M (magenta), C (cyan) and K (black) adopt the following known methods:
(1) A method in which four color toners are overlapped on a single photosensitive drum to form an image, and the image is transferred at a time,
(2) A transfer drum method in which a transfer medium is held on a transfer drum, and a four-color image is formed by four rotations of the transfer drum,
(3) An intermediate transfer body method in which a four-color image is formed on an intermediate transfer body, and the image is transferred on a transfer medium at a time, and
(4) A four-drum method in which four photosensitive bodies are disposed in parallel, and a four-color image is formed while a transfer medium is made to pass by the four photosensitive bodies (xe2x80x9csingle passxe2x80x9d).
In the four-drum type color image forming apparatus, color images formed on four parallel-arranged image carrying bodies are multiply transferred on a transfer medium by a single pass of the transfer medium. This apparatus is advantageous in that a color image can be formed in a quarter of the time needed in the other methods in four-color image forming processes. Therefore, high-speed operations can be performed by this apparatus.
A conventional color copying machine is equipped with a control panel having a density adjustment key for adjusting the density of an output image. Alternatively, the control panel has a key for selecting the kind of originals such as a character image, a character/photograph combination image and a photographic image. Alternatively, the control panel has a key for selecting the kind of sheets such as an ordinary sheet, a thick sheet, an OHP sheet and a postcard.
The density adjustment key functions to alter a development contrast potential or a tone curve correction coefficient. In accordance with the selection of the kind of the original, the image processing condition such as a screen structure is altered. In accordance with the selection of the kind of the sheet, the condition for transfer bias is altered. However, if there is a choice that does not belong to the specified classifications, the transfer bias condition cannot be altered.
In some apparatuses, the transfer bias condition is controlled according to the environment in which the apparatus is situated. Specifically, an environmental sensor provided in the apparatus senses the environment such as temperature and humidity, and the transfer bias condition is controlled in the sensed environment.
However, the change of the transfer bias condition is automatically controlled and cannot manually be adjusted by the user.
In the conventional color image formation apparatus, the control panel or display screen is equipped with a density adjustment key, a sheet kind selection key, an original kind selection key, a color balance adjustment key, etc. These keys provide user-controllable functions for obtaining better copy images (print images). Since so many parameters are associated with the color image formation process, these parameters can be made controllable.
In the conventional apparatus, a process condition for transferring a toner image on a transfer medium (more specifically a condition for a transfer bias applied to a transfer medium), which is one of color image formation processes, cannot manually be altered by the user""s (operator""s) operation of a switch key. Thus, a transfer process is performed under the same transfer bias condition for an original with high density and an original with low density.
Besides, when a sheet does not belong to specified classifications such as ordinary sheets or thick sheets, the transfer bias condition cannot be altered. Even if sheets to be used by the user belong to the classification of ordinary sheets, if the sheets are not the maker""s recommendable ones, optimal transfer bias conditions for the sheets cannot be selected.
Furthermore, if the actual environment of an apparatus differs from an environment sensed by an environment sensor of the apparatus, the transfer bias setting condition may differ from an optimal transfer bias condition. In such a case, an optimal transfer bias condition cannot be selected, and a better image quality cannot be obtained, In the industrial fields of printing and graphic designs, there is a demand for improved image quality adjustment in color image forming apparatuses.
The object of the present invention is to provide an image forming apparatus and an image forming system capable of adjusting a transfer bias condition and performing transfer under an optimal transfer bias condition, thus enhancing an image quality.
In order to achieve the object, this invention provides an image forming apparatus comprising: developing means for forming toner images on a plurality of image carrying bodies; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; setting means for setting transfer bias conditions of the plural transfer means; and control means for controlling bias voltages applied to the respective transfer means in accordance with the transfer bias conditions set by the setting means.
The invention provides an image forming apparatus comprising: read means for reading an image on an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; adjustment means for adjusting an image formation density of the original when the image on the original is read by the read means; first control means for controlling, when the image formation density of the original has been adjusted to a high density side by the adjustment means, the transfer bias conditions of the plural transfer means to confirm to high density transfer bias conditions; and second control means for controlling, when the image formation density of the original has been adjusted to a low density side by the adjustment means, the transfer bias conditions of the plural transfer means to confirm to low density transfer bias conditions.
The invention provides an image forming apparatus comprising: read means for reading an image on an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; switching means for switching a normal mode to a high print ratio image transfer mode in a case where, when the image on the original is read by the read means, the original is a high density image original or a high print ratio image original; and control means for controlling, when the normal mode has been switched to the high print ratio image transfer mode by the switching means, the transfer bias conditions of the plural transfer means to confirm to transfer bias conditions for the high print ratio image transfer mode.
The invention provides an image forming apparatus comprising: read means for reading an image on an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; select means for selecting one of a normal mode, a high print ratio image transfer mode and a highlight image transfer mode in accordance with the original when the image on the original is read by the read means; and control means for controlling the transfer bias conditions of the plural transfer means in accordance with the mode selected by the select means.
The invention provides an image forming apparatus comprising: read means for reading an image on an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; adjustment means for adjusting in multiple steps an image formation density of the original when the image on the original is read by the read means; and control means for controlling, when the image formation density of the original has been adjusted to a high density side or a low density side by the adjustment means, the transfer bias conditions of the plural transfer means in accordance with the adjustment step on the high density side or the adjustment step on the low density side.
The invention provides an image forming apparatus comprising: read means for reading an image by scanning an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; calculation means for calculating an average reflectance of the whole image of the original when the original is pre-scanned by the read means; and control means for performing a control to switch, when the average reflectance calculated by the calculation means is a predetermined first set value or less, transfer bias conditions of the plural transfer images to transfer bias conditions for a high density image, and to switch, when the average reflectance calculated by the calculation means is a second set value or more, which is different from the predetermined first set value, the transfer bias conditions of the plural transfer images to transfer bias conditions for a low density image.
The invention provides an image forming apparatus comprising: read means for reading an image by scanning an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; calculation means for calculating an average reflectance of the whole image of the original with respect to each of color components of yellow, magenta, cyan and black, when the original is pre-scanned by the read means; and control means for performing a control to switch, when the average reflectance calculated by the calculation means with respect to each of the color components of yellow, magenta, cyan and black is a predetermined first set value or less, transfer bias conditions of the plural transfer images to transfer bias conditions for a high density image, and to switch, when the average reflectance calculated by the calculation means with respect to each of the color components of yellow, magenta, cyan and black is a second set value or more, which is different from the predetermined first set value, the transfer bias conditions of the plural transfer images to transfer bias conditions for a low density image.
The invention provides an image forming system wherein a personal computer is connected to an image forming apparatus via a communication line to form an image, the personal computer comprising: display means for displaying a screen for controlling the image forming apparatus; and setting means for selecting and setting one of a high density image transfer mode and a low density image transfer mode associated with transfer bias conditions in the image forming apparatus, by means of the screen displayed on the display means for controlling the image forming apparatus, the image forming apparatus comprising: developing means for forming toner images on a plurality of image carrying bodies; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; and control means for controlling bias voltages applied to the transfer means on the basis of the transfer bias conditions associated with the high density image transfer mode or low density image transfer mode set by the setting means.
The invention provides an image forming apparatus comprising: read means for reading an image on an original; developing means for forming toner images on a plurality of image carrying bodies on the basis of the original image read by the read means; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; and control means for performing a control to switch, when a print ratio of the original read by the read means is a predetermined first print ratio or more, transfer bias conditions of the plural transfer images to transfer bias conditions for a high density image, and to switch, when the print ratio of the original read by the read means is a second print ratio or less, which is different from the predetermined first print ratio, the transfer bias conditions of the plural transfer images to transfer bias conditions for a low density image.
The invention provides an image forming apparatus, maintenance of which is controlled via a pre-connected communication line, the apparatus comprising: developing means for forming toner images on a plurality of image carrying bodies; a transfer belt for conveying a sheet, the transfer belt being disposed in contact with the image carrying bodies on which the toner images are formed by the developing means; a plurality of transfer means, provided at positions where the transfer belt is put in contact with the image carrying bodies, for transferring the toner images formed on the respective image carrying bodies onto the sheet conveyed by the transfer belt; and control means for controlling bias voltages applied to the respective transfer means in accordance with transfer bias conditions set by the control of the maintenance.